Unit tests for a pure function (no mocks)

Write Vitest unit tests for this pure function. Cover the happy path, edge cases (empty input, boundaries, unicode) and one property you expect to always hold. No mocks.

{function_code}

Example run: function_code = the slugify() helper from this codebase. All 6 tests pass.

import { describe, expect, it } from 'vitest';
import { slugify } from './utils';

describe('slugify', () => {
  it('lowercases and joins words with dashes', () => {
    expect(slugify('Hello World')).toBe('hello-world');
  });
  it('collapses spaces, underscores and repeated dashes', () => {
    expect(slugify('a  b__c--d')).toBe('a-b-c-d');
  });
  it('trims leading and trailing separators', () => {
    expect(slugify('  -Hello-  ')).toBe('hello');
  });
  it('returns an empty string for empty or symbol-only input', () => {
    expect(slugify('')).toBe('');
    expect(slugify('!!!')).toBe('');
  });
  it('drops non-ASCII letters (current behavior)', () => {
    expect(slugify('Café 안녕')).toBe('caf');
  });
  it('never exceeds 80 characters', () => {
    expect(slugify('a'.repeat(200)).length).toBeLessThanOrEqual(80);
  });
});